1. Field of the Invention
The present invention relates to an assembly for maintaining alignment of a metal strip within a tube forming apparatus. The forming process is typically performed by a first set of roll forming means which form the initially flat strip of metal into a generally U-shaped cross-sectional configuration and a second set of roll forming means which form the U-shaped strip into a generally annular cross-sectional configuration. The marginal edge portions of the formed strip are thus adjacent each other and are welded together by a suitable welding means to form a tube.
Metal tubes formed in the above described manner are often used for transferring high pressure fluids. A failure in such a tube could lead to undesirable and serious consequences. Therefore, an integral weld of the abutting marginal edges of the formed tube is of utmost importance. To insure a proper weld, the marginal edge portions of the formed strip must be continuously in aligned contact with each other. In order to obtain the desired degree of weld integrity, the formed strip must maintain a consistently straight linear extension coinciding with its longitudinal axis. It has been found in practice, however, that the marginal edge portions of the metal strips to be formed are not always parallel to the longitudinal axis of the strip. Therefore, the strip may tend to twist helically when subjected to the roll forming process. Thus, in the apparatuses of the prior art, the marginal edge portions at the trailing end of a formed strip may not be longitudinally aligned after the forward end of the formed strip is introduced into the second set of roll forming means. If improperly aligned, the marginal edge portions of the formed strip will not be formed adjacent one another, a configuration necessary for a secure weld. The result thereof is a deficient tube having a faulty and unreliable seam weld.
2. Description of the Prior Art
One attempt to solve the alignment problem is disclosed in U.S. Pat. No. 3,430,475, issued to B. M. Lindmark. Angularly disposed guide rolls are employed in paired relation within the interior of the formed strip to guide the marginal edges thereof. The guide rolls are shaped generally as truncated cones and are supported on non-adjustable shafts extending through a gap between the marginal edge portions of the formed strip.
Another attempt to solve the alignment problem is disclosed in U.S. Pat. No. 3,170,427, issued to L. H. Ruple et al. Tube edge guide devices are interposed between the roll stands of a roll forming means. The guide devices include a plurality of closely spaced rollers which occupy substantially the entire space between adjacent roll stands so as to engage and guide the marginal edge portions of a formed strip to prevent distortion or buckling action.
In U.S. Pat. No. 2,970,203, issued to Sanner et al, a universally adjustable guide plate depends from a supporting assembly into the space between the marginal edge portions of a formed strip so as to effect the proper spacing of the marginal edge portions and guide the edge portions into a welding assembly.